This invention relates to a method for automatic control of the voltage of an electrostatic filter at the breakdown limit by means of a time dependent increase of the filter voltage to breakdown and a subsequent breakdown dependent decrease.
A method of this general nature is described for example in German Patent Application DE-AS No. 11 48 977.
The degree of separation of an electrostatic separator is higher, the closer the operating voltage is to the flashover limit. Since flashover limit varies during operation as a function of several factors, such as, for example, gas composition, dust content and temperature, the voltage of the electrostatic separator must be regulated as a function of the level of the flashover limit.
In the method according to the above mentioned DE-AS No. 11 48 977, a control capacitor is charged across a resistance as a function of the filter current. A continuously variable tube which in turn is energized by a capacitor is connected in parallel with this control capacitor as a discharging resistance. This capacitor is charged in a breakdown dependent manner and is discharged continuously via a parallel resistance. The voltage at the control capacitor is used as a control voltage for a final control element on the primary side. The current dependence of the charging voltage for the control capacitor is chosen so that at low separator current strengths a relatively rapid voltage increase is obtained, and at high separator current strengths a relatively slow one. Through the constant discharge of the control capacitor dependent on the flashovers, the separator voltage after flashovers is lowered by an amount given by the number or duration of the flashovers.
In this control method, the prior history of the breakdown just then present enters in the voltage decrease or respectively the increase up to the breakdown limit as a relatively minor or largely undefined factor.